Like the 1980 census, the majority of households were enumerated in 1990 by mail. Questionnaires were delivered to every occupied housing unit. Households returned their completed questionnaires to the U.S. Census Bureau using the provided postage-paid envelope. Although the majority of households were counted by mail, the Census Bureau still employed approximately 510,000 enumerators to count hard-to-reach populations and households that did not return their questionnaire by mail.